1. Field of the Invention
The present invention relates generally to the maintenance of railroad tracks. More particularly, the present invention relates to a system and method for detecting tensile or compressive stress in railroad rails that are in use.
2. Related Art
The old-time “clickety clack” of railroad travel was caused by bolted joints in the rails, alternating left and right. These joints were usually 39 feet apart because the open-top gondola cars used for transporting new rails were 40 feet long, and rail segments were sized to fit these cars. In the early twentieth century, “continuous welded rail” (CWR) was invented, and the railroad companies began converting to CWR around 1950. Continuous welded rail typically comes in 440 yard (0.25 mile) segments which are spiked down to the crossties, and successive rail segments are then welded together in the field into “blocks” that are about two miles long. Where continuous welded rail is used, the only bolted joints are the ones at the ends of blocks, and these are electrically insulated to keep the adjoining track circuits separate.
As is well known, temperature changes cause metal, including railroad rails, to expand and contract, which presents several challenges for railroad maintenance. If the resulting forces from thermal expansion and con reactions are not properly controlled, rail joints can pull apart in the winter or rails can buckle in the summer, with what are called “sun kinks.” Pulled-apart rail joints and sun kinks can both derail a train. Unfortunately, systems and methods to assess internal rail stresses in railroad track in order to predict and thereby prevent track buckles and pull-aparts are inadequate in many respects.